This invention concerns broach pullers having clamping jaws used to grip a grooved end of a broaching tool in a broaching machine. Broaching machines function by pulling an elongated toothed broaching tool through or past a workpiece to form a particular feature on the workpiece with the broaching tool teeth.
A recurrent problem when broaching internal holes has involved the engagement of the clamping jaws with the annular groove on the end of the tool, which arises because a clearance is required to insure proper seating of the jaws. This clearance creates an axial end play, but the pulling action forces one side of the groove tightly against the jaws until the end of the stroke. A slight tool drop occurs at the end of the stroke which usually is not significant but in some circumstances creates problems, such as when broaching helical gear teeth in the workpiece when the slight drop will damage the part. The slight lost motion also creates inaccuracies as the proper relative rotative and axial position is lost.
One solution is to actuate the upper handler slide to place the tool in tension at all times, but this adds to the cost and complexity of the machine, as additional controls and programming are required. In two station machines additional cylinders are required for the handling slide, and also, when helical broaching, a lead bar is required.
Another approach is described in U.S. Pat. No. 4,180,360 issued on Dec. 25, 1979, for a "BROACHING PULLING MECHANISM" in which an axially aligned piston is provided in the puller, pressurized to be forced against the end of the tool to eliminate the axial clearance. This approach also obviously adds cost and complexity.
Yet another approach is shown in U.S. Pat. No. 4,859,125 issued on Aug. 22, 1989 for a "HELICAL BROACH PULLER" in which a pair of jaw sets engage either side of the annular groove to purportedly eliminates the end play. It is uncertain whether proper seating of both jaw sets can be reliably achieved by that design.
The object of the present invention is to provide a clamping jaw arrangement for a broach puller which eliminate axial end play by simple yet reliable means.